This invention is related to a robotic system with rigid body guidance or a robotic system with large deformation analysis (LDRS, i.e. semi-flexible and flexible robotic system) in robotics. A robotic system possesses the advanced properties to be one of the most important equipment in modem precision engineering. However, there are some serious technical barriers which have greatly dragged down the qualification of positioning accuracy of the technology for its general applications in precision engineering. The following degrading influences are considered as the major problems to cause such barriers:                The influence of tolerance and clearance;        The influence of the deformation of elements under load;        The influence of the change of load;        The influence of the wear of kinematic pair;        The influence of the ambient conditions, especially, the temperature; and        The influence of some associated problems with the gap of clearance and wear (i.e. backlash, contamination, and the thin film of lubrication, etc.).If these problems can be resolved, it will be easy for a robotic system to achieve the precise positioning accuracy or even ultra-precision positioning accuracy, and to claim its important role in modem precision engineering. The difficulty is that these degrading factors are inevitable with current understanding of the technology of robotics since they are associated with the nature of design, manufacturing, assembly, and application of a robotic system. Here, the positioning accuracy refers to the frame origin position and the frame orientation of the end-effecter of robot. As a result, to date, the positioning accuracy of a robot is relatively low. For example, in the development of a precise robotic computed tomography inspection system, a robotic system with the positioning accuracy in two-digital micrometer-level {0.001 in (0.025 mm), 5 arc-second} is urgently needed; however, on today's robotic market, such a precise robot is still unavailable.        
If a robotic system yielding rigid body analysis is not qualified to have precision positioning accuracy, then a robotic system yielding large deformation analysis (LDRS, i.e. the semi-flexible and the flexible robotic systems) is almost impossible to play a role in precision engineering. With a LDRS, all the above degrading problems exist; moreover, the problem of deformation becomes extremely serious. The uncertainties of nonlinear correlations of deformation make the LDRS too difficult to be controlled. By now, the technology of LDRS is still at its very early developing stage. Although a LDRS can have higher payload/weight ratio and better dynamic properties for limber motion, which are considered as the future direction of development of modem robotics, it is noted that no 6-D flexible robotic system has been developed yet in real application with the acceptable accuracy.
With investigation, it is found that many valuable efforts with academic researches and industrial practices have been done for the development of both the rigid-body robotic system and the LDRS. For simplification, the prior efforts can be classified into two different categories of control technology. The first is the category of direct control theory. For example, the robotic positioning control with finite element analysis, and the robotic positioning control based on real-time monitoring with embodied sensor on the elements to detect the deformation of linkage chain are the major efforts with this category. The direct control technology focuses on the understanding of the properties and characteristics of elements of the researched robotic system itself to explore the effective control. As above-mentioned, a robotic system with direct control suffers the influences of degrading factors, and it is difficult to achieve ultra-precision positioning accuracy.
The other can be classified as the category of indirect control theory. This technology tries to develop the effective control with the help of the target(s) or artificial marker(s) in the work-cell and some accessories that are not necessarily defined as part of the studied robotic system. The oldest indirect control of the robotic system is the tactile sensor system, which uses contact sensors to detect the position of the robotic system with the target(s) in work-cell as the reference to form closed-loop feedback control for positioning control. Currently, the most popular indirect control theory may be the visual servoing technology for robotic system control. Since this technology can form a non-contact closed-loop feedback control, it is getting its dominating position in the development of robotic system control. Generally, the visual servoing technology for robotic system control can be simplified in three different ways. The first is the on-body method. With this method, the visual sensor is mounted on the body of the robotic system to gather feedback control data. The second is the on-work-cell method. With this method, the visual sensor is mounted somewhere in the work cell to monitor the robotic system for gathering feedback-control data. The third is the combination of the above two ways. Currently, visual servoing technology of robotics is considered the main stream of robotic motion control. However, so far, visual servoing technology used in robotics can only control relatively simple objects undergoing constrained motion, or simple motion for complex objects. A majority of the visual servoing systems continue to employ artificial markers to circumvent the end-effecter and positioning data. The recent advances have allowed the development of theoretical frameworks for more complicated problems, the demonstration of real-time control for relative complex applications, and the construction of servoing systems that use no or very limited markers for the tracking process. However, the visual technology is still in developing process, and it is difficult for the technology to achieve the positioning accuracy in the micro-precision level at this stage.
Particularly, the following inventions and articles are also cited here as the close known prior arts and embodiments, which have presented some positioning technologies, or adopt some techniques in a robotic system design:
U.S. Pat. No. 6,730,541;
U.S. Pat. No. 6,144,118 A;
U.S. Pat. No. 6,744,228 B1 ;
U.S. Pat. No. 6,327,038;
Document No. US 2001/0044197; and
IEEE article “Task analysis of ultra-precision assembly process for automation of human skill.”
The article entitled “Task analysis of ultra-precision assembly process for automation of human skill” by Yamamoto et al. investigated how highly precision assembly could be done by using two methods, i.e., the force sensory information for a smaller range and the attitude measurement for a coarse range. The said development combined the indirect control methods of force sensory technology and visual servoing technology. Therefore, the said development required the target(s) or artificial marker(s) in work-cell as the reference to form a closed-loop feedback control, and it could only conduct simple tasks. Since the two combined methods can only provide relatively rough positioning control, the said invention did not conduct ultra-precision measurement and positioning control of a robotic system.
U.S. Pat. No. 6,730,541 and Document US 2001/0044197 to Heinen et al. presented a wafer-scale assembly apparatus for integrated circuits and a method for forming the wafer-scale assembly. The said invention did not provide a structure and method for the development of a multiple DOF robotic system to conduct ultra-precision measurement and positioning control.
U.S. Pat. No. 6,144,118 A and No. 6,744,228 B1 to Cahill et al. presented a high-speed positioning apparatus. It provided a planar positioning control with a small scale of range, which could not meet the basic requirement for the development of a multiple DOF robotic system in general in 6-DOF robotic working domain. In this invention, an interferometer encoder including the two-dimensional grid was used as position detector, which could not provide the ultra-precision absolute dimensional measurement for the development of a multiple DOF ultra-precision robotic system. Furthermore, the magnetic motor positioning technology adopted in this invention was also not able to achieve ultra-precision positioning accuracy. The said invention only provided 2-DOF planar measurement and positioning control, and did not conduct a rational structure and design methodology for the development of an ultra-precision multiple DOF (≧3) robotic system.
U.S. Pat. No. 6,327,038 to Maxey presented a method and apparatus which employed the interferometer system with an optical target to form a linear measurement device for measuring linear displacement and angular displacement. The said invention only provided relative linear displacement measurement along with the straight line of optical beam which was not suitable for the development of a robotic system since a robotic system relied on absolute displacement measurement in general. The said invention could not determine the angular displacement around the straight-line direction of optical beam (roll), and its capability to determine the angular displacements of target along with the pitch and yaw rotational directions was also limited. The said invention could not conduct a feasible real-time measurement since the relative linear displacement measurement with the presented device could only be done on expert's evaluation about the appearances of fringe in the ultra-precision measurement process. Moreover, the method and apparatus carried with the said invention provided a non-robust measurement technology since any slight change of working condition and interference of work-cell environment could very easily collapse the measurement process.
From the above discussions, the cited arts and inventions appear difficult to build a multiple DOF (≧3) robotic system to achieve ultra-precision positioning accuracy. It is also obvious that                The design methodologies of aforesaid related inventions and documents are not necessarily to develop a multiple DOF (≧3) ultra-precision shadow robotic measurement system that consists of linkages, kinematic joints, and sensors that are mated with the kinematic joints to form a passive servo-measurement system with proper DOF to monitor the position and orientation of an object with its own end-effecter through a connection-point.        The design methodologies of aforesaid related inventions and documents are not necessarily to develop an apparatus that integrates a multiple DOF (≧3) ultra-precision shadow robotic measurement system with a multiple DOF robot to establish a structure of closed-loop linkage chain to form a multiple DOF (≧3) ultra-precision robotic system that can achieve multiple DOF ultra-precision measurement and positioning control of end-effecter in 6-DOF (X, Y, Z, pitch, roll, and yaw) robotic working domain.        The design methodologies of aforesaid related inventions and documents are not necessarily to develop an apparatus to establish a closed-loop feedback control of a multiple DOF (≧3) ultra-precision robotic system associated with the said closed-loop linkage chain without the use and limitation of any target or artificial marker in work-cell as the reference.        
In such a situation, it calls for more ideas and innovative researches. It is therefore an object of this invention to develop a robotic system to have the capability to achieve ultra-precision positioning accuracy to overcome the above-said influences of the degrading factors to claim the important role of robotic system in modem ultra-precision engineering.